In recent years, the applications of magnetic recording devices such as magnetic disk drives, floppy (registered trademark) disk drives, and magnetic tape drives have remarkably increased, and the importance of the magnetic recording devices has increased.
In particular, high densification of the surface recording density has increased considerably with the introduction of the MR head (MagnetoResistive head), PRML (Partial Response Maximum Likelihood) technology, the GMR head (Giant MagnetoResistive head), the TMR head (Tunnel MagnetoResistive head), and the like.
Thereby, there has been a demand for an even higher recording density to be achieved in the magnetic recording medium applied to the above-mentioned magnetic recording device. For this reason, there has been a need for a magnetic recording medium having a higher coercive force and a high S/N ratio (ratio obtained by dividing the signal amount by the noise amount).
Moreover, in the magnetic recording medium of recent years, the film thickness of the medium has been reduced in order to achieve the high surface recording density. For this reason, there is a phenomenon that the recorded magnetization is weakened due to thermal disturbance. Particularly, there is a great technical problem for the thermal stability of magnetic recording.
Among other things, when the S/N ratio increases, thermal stability of the recorded magnetization often decreases. This is because generally the medium having a high S/N ratio often has a minute crystal grain size of magnetic grains included in a magnetic recording layer, which is effective for the medium noise, but on the other hand, becomes close to an unstable region in terms of thermal stability of magnetism.
Moreover, in recent years, efforts have been maintained to raise the surface recording density with an increase in the track density, and in the magnetic recording device, the track density has reached 350 kTPI.
However, when the track density is raised, magnetic recording information between the adjacent tracks interferes with each other. Therefore, a problem easily occurs in which a magnetization transition region located at the boundary region thereof becomes a noise source and thus the S/N ratio decreases.
Occurrence of such a problem leads to a decrease in the bit error rate, which becomes an obstacle to the improvement of the recording density.
In addition, as the distance between the tracks comes closer, an extremely high-accuracy track servo technique is required for the magnetic recording device.
Moreover, in the magnetic recording device, a method is generally used in which the recording is executed widely and the reproduction narrower than at the time of recording in order to eliminate the influence from the adjacent track as much as possible is executed. In this method, the influence between the tracks can be suppressed to the minimum, but on the other hand, it is difficult to sufficiently obtain a reproduction output, which results in a difficulty in securing the S/N ratio having a sufficient size.
A perpendicular magnetic recording medium has been used in recent years in order to secure thermal stability of the medium as mentioned above.
In order to achieve higher recording densification even in the perpendicular magnetic recording, it is necessary to increase the track density. In addition, in the perpendicular magnetic recording medium, it is necessary to reduce the recording blur (fringe) of the recording end which causes a problem by increasing the track density.
An example of a method of solving this fringe includes a discrete medium (see, for example, Japanese Unexamined Patent Application Publication Nos. H6-259709 and H9-97419).
Japanese Unexamined Patent Application Publication No. H6-259709 discloses a structure of a discrete medium in which a data section is formed of a projection portion and a nonmagnetic section is formed of a recess portion. However, provision of a recess portion-type nonmagnetic section causes irregularities to exist on the disk surface, and thus is not preferable due to an adverse effect on the levitation of a recording/reproducing head.
Japanese Unexamined Patent Application Publication No. H9-97419 discloses a method of forming a magnetic recording layer on a glass disk substrate, forming a groove for disposing a magnetic recording section and a nonmagnetic section by patterning the magnetic recording layer, then forming a nonmagnetic film (film used as a base material of the nonmagnetic section) so as to fill the groove by a sputtering method, and thereafter forming the nonmagnetic section in the groove by removing a portion located above the upper surface of the magnetic recording section in the nonmagnetic film by ion beam etching.
In addition, it discloses that an oxide, a nitride, a carbide, a boride, a polymeric compound, and the like are used as a material of the nonmagnetic film.
However, when the nonmagnetic film is formed by a sputtering method using materials such as the above-mentioned oxide, nitride, carbide, boride, or polymeric compound, the thicknesses of the nonmagnetic films formed on a plurality of magnetic recording sections are different from each other depending on the shapes of the magnetic recording sections (for example, widths or areas when seen in a plan view).
For this reason, when the nonmagnetic section is formed by removing the nonmagnetic film until the surfaces of a plurality of magnetic recording sections are exposed by ion beam etching, the surface of the nonmagnetic film included in the nonmagnetic section becomes lower than the surface of the magnetic recording section (a recess is generated), and the irregularities are formed on the surface composed of the surface of the magnetic recording section and the surface of the nonmagnetic film in which ion beam etching is performed (hereinafter, referred to as the “etched surface”), whereby there has been a problem that the surface of the magnetic recording medium cannot be formed smoothly.
When such a magnetic recording medium having no smooth surface is incorporated into the magnetic recording/reproducing device, there has been a concern that the magnetic head may become broken, or a concern that the magnetic recording/reproducing device may not operate normally.
In addition, when the nonmagnetic film is formed using the sputtering method which does not have preferable filling characteristics, a gap is formed between the nonmagnetic section and the magnetic recording section, whereby there has been a problem in that the magnetic recording medium corrodes from the above-mentioned gap due to the environment of use of the magnetic recording/reproducing device.
The related art aimed at improving such a problem of Japanese Unexamined Patent Application Publication No. H9-97419 includes Japanese Unexamined Patent Application Publication No. 2005-100496.
Japanese Unexamined Patent Application Publication No. 2005-100496 discloses a method of applying an ultraviolet curable resin as a nonmagnetic film so as to fill a groove by a spin coating method, curing the ultraviolet curable resin by ultraviolet irradiation, and thereafter forming a nonmagnetic section in the groove by removing an unnecessary portion of the ultraviolet curable resin through ion beam etching.
In this manner, it is possible to suppress the formation of a gap between the groove and the ultraviolet curable resin by filling the ultraviolet curable resin into the groove using the spin coating method having filling characteristics superior to that of the sputtering method. That is, it is possible to suppress the corrosion of the magnetic recording medium from the above-mentioned gap.
In addition, it is possible to reduce the irregularities formed in the etched surface, further than in the case where the nonmagnetic section is formed by the method disclosed in Japanese Unexamined Patent Application Publication No. H9-97419, by forming the nonmagnetic section by the method disclosed in Japanese Unexamined Patent Application Publication No. 2005-100496.
However, when the ultraviolet curable resin is spin-coated on the surface of the magnetic layer (magnetic recording section) of which the irregularities are processed by the method disclosed in Japanese Unexamined Patent Application Publication No. 2005-100496, there may be a case where the irregularities (for example, the irregularities having a size of approximately 10 nm) are formed on the surface of the ultraviolet curable resin due to the shape of the magnetic recording section or non-uniformity of the ultraviolet curable resin (specifically, for example, non-uniformity of distribution of components included in the ultraviolet curable resin). Such irregularities may be generated by the influence of surface tension of the resin in the projection-shaped magnetic recording section, and are formed on the surface of the resin even in the case where a resin other than the ultraviolet curable resin is used.
In addition, there has been a problem in that the curing rate of the ultraviolet curable resin becomes non-uniform in the film. In particular, the curing rate in the surface of the film is high. On the other hand, the curing rate of the resin buried in the recess portion of the magnetic layer is low, whereby the distortion occurs within the cured ultraviolet curable resin, which results in the occurrence of a recess in the nonmagnetic section (resin buried in the recess portion of the magnetic layer) at the time of planarizing a resin layer.
As a method of reducing such irregularities formed on the surface of the resin, it is considered that the thickness of the resin is increased. However, when the thickness of the resin is increased, the thickness of the resin to be removed by ion beam etching increases, and thus the etching time is prolonged. When ion beam etching is performed for a long time, the etched surface of the nonmagnetic film is roughened, and thus the surface of the magnetic recording medium cannot be formed smoothly.
In addition, it is also considered that the surface tension of the resin in the projection-shaped magnetic recording section is lowered by lowering the viscosity of the resin. However, this narrows the range of choices for the resin capable of being used as a filling material.